|XENODM(1)||General Commands Manual||XENODM(1)|
xenodm — X Display
xenodm manages a collection of X displays
on the local host.
xenodm provides services similar
to those provided by getty(8)
and login(1) on character
terminals: prompting for login name and password, authenticating the user,
and running a “session”.
A “session” is defined by the lifetime of a
particular process; in the traditional character-based terminal world, it is
the user's login shell. In the
xenodm context, it is
an arbitrary session manager. This is because in a windowing environment, a
user's login shell process does not necessarily have any terminal-like
interface with which to connect. When a real session manager is not
available, a window manager or terminal emulator is typically used as the
“session manager”, meaning that termination of this process
terminates the user's session.
When the session is terminated,
resets the X server and (optionally) restarts the whole process.
xenodm provides the first
interface that users will see, it is designed to be simple to use and easy
to customize to the needs of a particular site.
xenodm has many options, most of which have
reasonable defaults. Browse through the various sections of this manual,
picking and choosing the things you want to change. Pay particular attention
to the SESSION PROGRAM section,
which will describe how to set up the style of session desired.
xenodm is highly configurable, and most of
its behavior can be controlled by resource files and shell scripts. The
names of these files themselves are resources read from the file
xenodm-config or the file named by the
xenodm can manage X servers running on the
local machine and specified in Xservers.
The resources of the X clients run by
xenodm outside the user's session, including
xenodm's own login window, can be affected by
setting resources in the Xresources file.
After resetting the X server,
the Xsetup script to assist in setting up the screen
the user sees along with the xlogin widget.
The xlogin widget, which
offers the familiar login and password prompts, unless
autoLogin is set.
After the user logs in,
xenodm runs the
Xstartup script as root.
xenodm runs the
Xsession script as the user. This system session
file may do some additional startup and typically runs the
.xsession script in the user's home directory. When
the Xsession script exits, the session is over.
At the end of the session, the Xreset script is run to clean up, the X server is reset, and the cycle starts over.
The file /var/log/xenodm.log will contain
error messages from
xenodm and anything output to
stderr by Xsetup,
Xstartup, Xsession or
Xreset. When you have trouble getting
xenodm working, check this file to see if
xenodm has any clues to the trouble.
All of these options, except
itself, specify values that can also be specified in the configuration file
xenodm. /etc/X11/xenodm/xenodm-config is the default. See the section CONFIGURATION FILE.
falseas the value for the
DisplayManager.daemonModeresource. This suppresses the normal daemon behavior, which is for
xenodmto close all file descriptors, disassociate itself from the controlling terminal, and put itself in the background when it first starts up.
DisplayManager.debugLevelresource. A non-zero value causes
xenodmto print lots of debugging statements to the terminal; it also disables the
xenodmto run synchronously. To interpret these debugging messages, a copy of the source code for
xenodmis almost a necessity. No attempt has been made to rationalize or standardize the output.
DisplayManager.errorLogFileresource. This file contains errors from
xenodmas well as anything written to
stderrby the various scripts and programs run during the progress of the session.
DisplayManager*resourcesresource. This file is loaded using xrdb(1) to specify configuration parameters for the authentication widget.
DisplayManager.serversresource. See the section LOCAL SERVER SPECIFICATION for a description of this resource.
DisplayManager*sessionresource. This indicates the program to run as the session after the user has logged in.
At many stages the actions of
be controlled through the use of its configuration file, which is in the X
resource format. Some resources modify the behavior of
xenodm on all displays, while others modify its
behavior on a single display. Where actions relate to a specific display,
the display name is inserted into the resource name between
“DisplayManager” and the final resource name segment.
For local displays, the resource name and class are as read from the Xservers file.
Because the resource manager uses colons to separate the name of
the resource from its value and dots to separate resource name parts,
xenodm substitutes underscores for both dots and
colons when generating the resource name. For example,
DisplayManager.expo_x_org_0.startup is the name of
the resource which defines the startup shell file for the
stderrby the Xsetup, Xstartup, Xsession and Xreset files, so it will contain descriptions of problems in those scripts as well.
xenodm, which would normally not be useful.
xenodmattempts to make itself into a daemon process unassociated with any terminal. This is accomplished by forking and leaving the parent process to exit, then closing file descriptors and releasing the controlling terminal. In some environments this is not desired (in particular, when debugging). Setting this resource to
falsewill disable this feature.
xenodmstores authorization files while initializing the session. The default value is /etc/X11/xenodm. Can be overridden for specific displays by
xenodmrescans the configuration, servers, access control and authentication keys files after a session terminates and the files have changed. By default it is
true. You can force
xenodmto reread these files by sending a
SIGHUPto the main process.
xenodmwhen attempting to open intransigent servers.
openDelayis the length of the pause in seconds between successive attempts,
openRepeatis the number of attempts to make,
openTimeoutis the amount of time to wait while actually attempting the open (i.e., the maximum time spent in the connect(2) system call) and
startAttemptsis the number of times this entire process is done before giving up on the server. After
openRepeatattempts have been made, or if
openTimeoutseconds elapse in any particular attempt,
xenodmterminates and restarts the server, attempting to connect again. This process is repeated
startAttemptstimes, at which point the display is declared dead and disabled. Although this behavior may seem arbitrary, it has been empirically developed and works quite well on most systems. The bound
reservAttemptsis the number of times a successful connect is allowed to be followed by a fatal error. When reached, the display is disabled. The default values are
startAttempts: 4 and
PATHenvironment variable for the session to this value. It should be a colon separated list of directories; see sh(1) for a full description. The default value is “/bin:/usr/bin:/sbin:/usr/sbin:/usr/X11R6/bin:/usr/local/bin:/usr/local/sbin”.
PATHenvironment variable for the startup and reset scripts to the value of this resource. The default for this resource is “/sbin:/usr/sbin:/bin:/usr/bin:/usr/X11R6/bin”. Note the absence of ‘
.’ from this entry. This is a good practice to follow for root; it avoids many common Trojan Horse system penetration schemes.
SHELLenvironment variable for the startup and reset scripts to the value of this resource. It is /bin/sh by default.
xenodmwill fall back to this program. This program is executed with no arguments, but executes using the same environment variables as the session would have had (see the section SESSION PROGRAM). By default, /usr/X11R6/bin/xterm is used.
xenodmgrabs the server and keyboard while reading the login name and password. The
grabServerresource specifies if the server should be held for the duration of the name/password reading. When
false, the server is ungrabbed after the keyboard grab succeeds, otherwise the server is grabbed until just before the session begins. The default is
grabTimeoutresource specifies the maximum time
xenodmwill wait for the grab to succeed. The grab may fail if some other client has the server grabbed, or possibly if the network latencies are very high. This resource has a default value of 3 seconds; you should be cautious when raising it, as a user can be spoofed by a look-alike window on the display. If the grab fails,
xenodmkills and restarts the server (if possible) and the session.
authorizeis a boolean resource which controls whether
xenodmgenerates and uses authorization for the local server connections. If authorization is used,
authNameis a list of authorization mechanisms to use, separated by white space. When
authorizeis set for a display and authorization is not available, the user is informed by having a different message displayed in the login widget. By default, Ic authorize is
authNameis “MIT-MAGIC-COOKIE-1”, or, if XDM-AUTHORIZATION-1 is available, “XDM-AUTHORIZATION-1 MIT-MAGIC-COOKIE-1”.
xenodmto the server, using the
-authserver command line option. It should be kept in a directory which is not world-writable as it could easily be removed, disabling the authorization mechanism in the server. If not specified, a name is generated from DisplayManager.authDir and the name of the display.
false, disables the use of the
unsecureGreetingin the login window. See the section AUTHENTICATION WIDGET. The default is
xenodmsends to reset the server. See the section CONTROLLING THE SERVER. The default is 1 (
xenodmsends to terminate the server. See the section CONTROLLING THE SERVER. The default is 15 (
xenodmgenerates the authorization information just before connecting to the display, an old server would not get up-to-date authorization information. This resource causes
SIGHUPto the server after setting up the file, causing an additional server reset to occur, during which time the new authorization information will be read. The default is
false, which will work for all MIT servers.
xenodmis unable to write to the usual user authorization file ($HOME/.Xauthority), it creates a unique file name in this directory and points the environment variable
XAUTHORITYat the created file. It uses /tmp by default.
xenodm configuration file
should be set up. Make a directory (usually
/etc/X11/xenodm) to contain all of the relevant
Here is a reasonable configuration file, which could be named xenodm-config:
DisplayManager.servers: /etc/X11/xenodm/Xservers DisplayManager.errorLogFile: /var/log/xenodm.log DisplayManager*resources: /etc/X11/xenodm/Xresources DisplayManager*startup: /etc/X11/xenodm/Xstartup DisplayManager*session: /etc/X11/xenodm/Xsession DisplayManager._0.authorize: true DisplayManager*authorize: false
Note that this file mostly contains references to other files.
Note also that some of the resources are specified with
*’ separating the components. These
resources can be made unique for each different display, by replacing the
*’ with the display-name, but
normally this is not very useful. See the
RESOURCES section for a complete
a server specification or, if the value starts with a slash
/’), the name of a file containing
server specifications, one per line.
Each specification indicates a display which should constantly be
managed. If the resource or the file named by the resource is empty,
xenodm will exit.
Each specification consists of at least three parts: a display name, a display class, a display type, and a command line to start the server. A typical entry for local display number 0 would be:
The only recognized display type is:
The display name must be something that can be passed in the
-display option to an X program. This string is used
to generate the display-specific resource names, so be careful to match the
names (e.g., use “:0 local /usr/X11R6/bin/X :0” instead of
“localhost:0 local /usr/X11R6/bin/X :0” if your other
resources are specified as “DisplayManager._0.session”). The
display class portion is also used in the display-specific resources, as the
class of the resource. This is useful if you have a large collection of
similar displays (such as a corral of X terminals) and would like to set
resources for groups of them.
xenodm starts a session, it sets up
authorization data for the server. For local servers,
xenodm passes “
filename” on the server's command line to point
it at its authorization data.
The Xresources file is loaded onto the display as a resource database using xrdb(1). As the authentication widget reads this database before starting up, it usually contains parameters for that widget:
xlogin*login.translations: #override\ Ctrl<Key>R: abort-display()\n\ <Key>F1: set-session-argument(failsafe) finish-field()\n\ <Key>Return: set-session-argument() finish-field() xlogin*borderWidth: 3 xlogin*greeting: CLIENTHOST #ifdef COLOR xlogin*greetColor: CadetBlue xlogin*failColor: red #endif
Please note the translations entry; it specifies a few new translations for the widget which allow users to escape from the default session (and avoid troubles that may occur in it). Note that if #override is not specified, the default translations are removed and replaced by the new value, not a very useful result as some of the default translations are quite useful (such as “<Key>: insert-char ()” which responds to normal typing).
This file may also contain resources for the setup program.
The Xsetup file is run after the server is reset, but before the Login window is offered. The file is typically a shell script. It is run as root, so should be careful about security. This is the place to change the root background or bring up other windows that should appear on the screen along with the Login widget.
In addition to any specified by
DisplayManager.exportList, the following environment
variables are passed:
Note that since
xenodm grabs the keyboard,
any other windows will not be able to receive keyboard input. They will be
able to interact with the mouse, however; beware of potential security holes
is set, Xsetup will not be able to connect to the
display at all. Resources for this program can be put into the file named by
Here is a sample Xsetup script:
#!/bin/sh # Xsetup_0 - setup script for one workstation xcmsdb < /etc/X11/xenodm/monitors/alex.0 xconsole -geometry 480x130-0-0 -notify -verbose -exitOnFail &
The authentication widget prompts the user for the username,
password, and/or other required authentication data from the keyboard.
Nearly every imaginable parameter can be controlled with a resource.
Resources for this widget should be put into the file named by
All of these have reasonable default values, so it is not necessary to
specify any of them.
The resource file is loaded with xrdb(1) so it may use the substitutions defined by that program such as CLIENTHOST for the client hostname in the login message, or C pre-processor #ifdef statements to produce different displays depending on color depth or other variables.
xenodm is compiled with support for the
Xft(3) library for font
rendering. Font faces are specified using the resources with names ending in
“face” in the fontconfig face format described in the
“Font Names” section of
true, when built with XPM support, attempt to use the X Non-Rectangular Window Shape Extension to set the window shape. The default is
hiColoris the highlight color, used on the top and left sides of the frame, and the bottom and right sides of text input areas.
shdColoris the shadow color, used on the bottom and right sides of the frame, and the top and left sides of text input areas. The default for both is the foreground color, providing a flat appearance.
frameWidthis the width in pixels of the area around the greeter frame drawn in
innerFramesWidthis the width in pixels of the area around text input areas drawn in
sepWidthis the width in pixels of the bezeled line between the greeting and input areas drawn in
false, don't allow root (and any other user with uid = 0) to log in directly. The default is
true. This setting is only checked by some of the authentication backends at this time.
true, allow an otherwise failing password match to succeed if the account does not require a password at all. The default is
false, so only users that have passwords assigned can log in.
true, a placeholder character (
echoPasswdChar) will be shown for fields normally set to not echo, such as password input. The default is
echoPasswdis true. The default is ‘
*’. If set to an empty value, the cursor will advance for each character input, but no text will be drawn.
Ctrl<Key>H: delete-previous-character() \n\ Ctrl<Key>D: delete-character() \n\ Ctrl<Key>B: move-backward-character() \n\ Ctrl<Key>F: move-forward-character() \n\ Ctrl<Key>A: move-to-begining() \n\ Ctrl<Key>E: move-to-end() \n\ Ctrl<Key>K: erase-to-end-of-line() \n\ Ctrl<Key>U: erase-line() \n\ Ctrl<Key>X: erase-line() \n\ Ctrl<Key>C: restart-session() \n\ Ctrl<Key>\\: abort-session() \n\ <Key>BackSpace: delete-previous-character() \n\ <Key>Delete: delete-previous-character() \n\ <Key>Return: finish-field() \n\ <Key>: insert-char() \
The actions which are supported by the widget are:
xenodmstarts the session. Otherwise the failure message is displayed and the user is prompted again.
xenodmon a system console, such as when shutting the system down, when using xdmshell(1), to start another type of server, or to generally access the console. Sending
SIGHUPwill restart the display. See the section CONTROLLING XENODM.
xenodm. Be very careful using this; it might be better to disconnect the machine from the network before doing this.
On some systems (OpenBSD) the user's shell must be listed in /etc/shells to allow login through xenodm. The normal password and account expiration dates are enforced too.
The Xstartup program is run as root when the user logs in. It is typically a shell script. Since it is run as root, Xstartup should be very careful about security. This is the place to put commands which add entries to utmp(5) or wtmp(5) files (the sessreg(1) program may be useful here), mount users' home directories from file servers, or abort the session if logins are not allowed.
In addition to any specified by
DisplayManager.exportList, the following environment
variables are passed:
No arguments are passed to the script.
xenodm waits until this script exits before starting
the user session. If the exit value of this script is non-zero,
xenodm discontinues the session and starts another
The sample Xstartup file shown here prevents login while the file /etc/nologin exists. Thus this is not a complete example, but simply a demonstration of the available functionality.
Here is a sample Xstartup script:
#!/bin/sh # # Xstartup # # This program is run as root after the user is verified # if [ -f /etc/nologin ]; then xmessage -file /etc/nologin -timeout 30 -center exit 1 fi sessreg -a -l $DISPLAY -x /etc/X11/xenodm/Xservers $LOGNAME /etc/X11/xenodm/GiveConsole exit 0
The Xsession program is the command which is run as the user's session. It is run with the permissions of the authorized user.
In addition to any specified by
DisplayManager.exportList, the following environment
variables are passed:
At most installations, Xsession should look in $HOME for a file .xsession, which contains commands that each user would like to use as a session. Xsession should also implement a system default session if no user-specified session exists.
An argument may be passed to this program from the authentication
widget using the
set-session-argument action. This
can be used to select different styles of session. One good use of this
feature is to allow the user to escape from the ordinary session when it
fails. This allows users to repair their own
.xsession if it fails, without requiring
administrative intervention. The example following demonstrates this
This example recognizes the special failsafe mode, specified in the translations in the Xresources file, to provide an escape from the ordinary session. It also requires that the .xsession file be executable so we don't have to guess what shell it wants to use.
#!/bin/sh # # Xsession # # This is the program that is run as the client # for the display manager. case $# in 1) case $1 in failsafe) exec xterm -geometry 80x24-0-0 ;; esac esac startup=$HOME/.xsession resources=$HOME/.Xresources if [ -f "$startup" ]; then exec "$startup" else if [ -f "$resources" ]; then xrdb -load "$resources" fi twm & xman -geometry +10-10 & exec xterm -geometry 80x24+10+10 -ls fi
The user's .xsession file might look something like this example. Don't forget that the file must have execute permission.
#! /bin/csh # no -f in the previous line so .cshrc gets run to set $PATH twm & xrdb -merge "$HOME/.Xresources" emacs -geometry +0+50 & xbiff -geometry -430+5 & xterm -geometry -0+50 -ls
Symmetrical with Xstartup, the Xreset script is run after the user session has terminated. Run as root, it should contain commands that undo the effects of commands in Xstartup, updating entries in utmp(5) or wtmp(5) files, or unmounting directories from file servers. The environment variables that were passed to Xstartup are also passed to Xreset.
A sample Xreset script:
#!/bin/sh # # Xreset # # This program is run as root after the session ends # sessreg -d -l $DISPLAY -x /etc/X11/xenodm/Xservers $LOGNAME /etc/X11/xenodm/TakeConsole exit 0
xenodm controls local servers using POSIX
SIGHUP is expected to reset the server,
closing all client connections and performing other cleanup duties.
SIGTERM is expected to terminate the server. If
these signals do not perform the expected actions, the resources
can specify alternate signals.
xenodm responds to two signals:
rereads the configuration file, the access control file, and the servers
file. For the servers file, it notices if entries have been added or
removed. If a new entry has been added,
starts a session on the associated display. Entries which have been removed
are disabled immediately, meaning that any session in progress will be
terminated without notice and no new session will be started.
When sent a
xenodm terminates all sessions in progress and
exits. This can be used when shutting down the system.
xenodm attempts to mark its various
sub-processes for ps(1) by
editing the command line argument list in place. Because
xenodm can't allocate additional space for this
task, it is useful to start
xenodm with a reasonably
long command line (using the full path name should be enough). Each process
which is servicing a display is marked
To add an additional local display, add a line for it to the Xservers file. (See the section LOCAL SERVER SPECIFICATION.)
Examine the display-specific resources in
DisplayManager._0.authorize) and consider which of
them should be copied for the new display. The default
xenodm-config has all the appropriate lines for
displays :0 and :1.
You can use
xenodm to run a single session
at a time, using the 4.3
init(8) options or other
suitable daemon by specifying the server on the command line:
One thing that
xenodm isn't very good at
doing is coexisting with other window systems. To use multiple window
systems on the same hardware, you'll probably be more interested in
xenodmstores keys for clients to read
X Display Manager Control Protocol.
R. Hinden and S. Deering, IP Version 6 Addressing Architecture, RFC 4291, February 2006.
Keith Packard, MIT X Consortium
|March 4, 2017||xenodm 0.1 X Version 11|